Dominique Strauss-Kahn votes in the first round of the 2012 French presidential election at a polling station in Sarcelles today. (REUTERS)

PARIS — Socialist champion Francois Hollande stamped his authority on the French presidential race Sunday, winning the first round of polling and setting up a May 6 runoff with incumbent Nicolas Sarkozy.

Hollande won between 28 and 30 percent of the vote in the first round, to Sarkozy’s 24 to 27.5, according to estimates compiled from ballot samples by several polling agencies and obtained by AFP from multiple sources.

That made Sarkozy the only incumbent French president to lose a first round-vote in the history of the Fifth Republic, which came into being in 1958.

“It’s a very good first round score. Dignity paid off,” said Socialist spokeswoman Aurelie Filippetti, welcoming Sunday’s result in the more upbeat venues of Hollande’s party headquarters.

Le Pen came third with between 17 and 20 percent, beating bitter enemy Melenchon, who scored between 10.5 and 13 percent. Bayrou won between 8.7 and 10 percent, according to the estimates seen by AFP.

Turnout was high at about 80 percent — down on the 84 percent turnout of 2007 but up significantly on the 72 percent of 2002 and belying fears that a low-key campaign would be capped by mass abstention.

The left has not won a presidential election in a quarter of a century, but with France mired in low growth and rising joblessness, opinion polls had long predicted that the left would beat the right-wing incumbent.

Hollande says Sarkozy has trapped France in a downward spiral of austerity and job losses, while Sarkozy says his rival is inexperienced and weak-willed and would spark financial panic through reckless spending pledges.

The eurozone debt crisis and France’s sluggish growth and high unemployment have hung over the campaign, with Sarkozy struggling to defend his record and Hollande unable to credibly promise spending increases.

“I have never missed a vote, but this time I feel little enthusiasm for the election,” said 62-year-old retired high school teacher Isabelle Provost as she emerged into bright Paris sunshine after casting her ballot.

“Economically there is little difference between the two main candidates,” she said, echoing the sentiment of many others of the right and the left.

Opinion polls and campaigning were banned from midnight on Friday, and will resume on Monday in the build-up to the May 6 runoff, which Hollande is predicted to win by around 55 percent to 45.

Sarkozy and Hollande face a two-week scramble for the finish line, including a head-to-head televised debate that could be the incumbent’s last chance to change his fortunes.

Privately however, Sarkozy’s top supporters had begun to admit that if Sarkozy failed to regain the momentum and slip ahead of Hollande on Sunday, he would have too much ground left to make up.